MRA of the Head (Circle of Willis)
Basics: What is an MRA of the Head?
MRA stands for “magnetic resonance angiography”. In short, MRA of the head is a relatively quick (20 minutes), extremely accurate noninvasive test to get a close look at the arteries in your head. It is extremely good at finding narrowed arteries (stenosis), brain aneurysms, fistulas, and arterovenous malformations, with stenosis and aneurysms of the intracranial arteries being more common blood vessel pathologies in the head which can be fixed, otherwise leading to potentially devastating strokes and/or death.
Do you have to put an IV in to inject dye for a standard MRA of the head?
No. However, there is a specialized type of MRA of the head used to evaluate patients who have already been treated for aneurysms or stenosis, which does use contrast, to provide increased sensitivity.
We provide the most accurate MRA of the head of anywhere in the entire USA, outside of a pure research environment. This is because we have: 1) the most powerful magnetic field, (3 Tesla), 2) a special head coil (12 channels), which provides the highest resolution images, and 3) We intentionally set up the test to take the finest detailed images. It takes longer, and requires more patience and skill on the part of our technologists, but we believe it is worth it. Additionally, we cover a larger area of the brain and are able to clearly visualize smaller vessels that other centers are not able to do. We are the only center in the NW that routinely can accurately evaluate for a more unusual problem called dural fistulas in the extracranial carotid circulation. In addition we do extensive post processing for many subtle abnormalities. The procedure takes 20 minutes or less and requires no intravenous contrast. Our slice thicknesses are 0.5 mm or less, unless we are doing a “screening MRA” which is 0.7 mm.
Answers to additional commonly asked questions about MRA of the head:
Q: How do I decide whether to get an MRA or a CTA?
A: In general, we prefer an MRA instead of a CTA for most problems. MRA does not use radiation, and CTA does. In addition, MRA automatically subtracts out the bones of the skull base, which makes CTA more time consuming to read. I believe in general, there is more potential for even a fellowship-trained neuroradiologist to miss some subtle findings with a CTA that they wouldn’t miss on an MRA. Reasons to get a CTA in some cases may include: Small arterial lesions away from the main arteries of the skull base such as Arterovenous Malformations (AVMs), unusual problems involving the veins (fistulas with venous varices), and most importantly — suspicion of thrombus/clot in the dural sinuses (larger deep veins at the base of the skull) may be reasons to get a CTA instead. Often a blood vessel problem is seen with MRA, and CTA can confirm the finding and then provide additional or complimentary information.
Discussion of images above:
The above images demonstrate our standard MRA study of the head. It is a normal study. Our dictation for this study is as follows:
There is codominance of the anterior cerebral territories with a patent anterior communicating artery. The bilateral distal cervical carotid arteries, as well as intracranial internal carotid arteries, and middle cerebral arteries are normal. The posterior circulation is left vertebral dominant. The left posterior communicating artery is generous. The right posterior communicating artery is visualized. No aneurysms, stenoses, or vascular malformations.
"I have personally read more than 5000 MRA exams, and I believe that no one in the country provides a more accurate and/or sensitive MRA exam."
— David A. Siker MD